The present invention is directed to the measurement of fluid flow in a conduit, particularly by detection and measurement of energy directed through the fluid.
It is known in the art to monitor fluid flow through a conduit by detecting and measuring a beam of, e.g., ultrasonic, energy traversing the fluid. One known technique of this type involves the disposition of an obstruction in the flow path upstream of the path of an ultrasonic beam through the fluid. The obstruction produces vortices having a fixed mutual spacing, regardless of fluid flow velocity, so that the frequency with which such vortices pass through an ultrasonic beam will be indicative of flow velocity. Measurement devices utilizing this principle are disclosed, for example, in U.S. Pat. Nos. 3,680,375; 3,881,352; and 3,886,794.
It will be appreciated that implementation of this technique requires the installation of an obstructing device, such as a vortex strut, in the fluid stream and when the fluid to be monitored is flowing in a conduit, installation of the strut entails added manufacturing costs or retrofitting costs if flow measurement equipment is to be installed in an existing system. It is also known to monitor fluid flow in a conduit, utilizing ultrasonic energy, without the aid of an obstruction or strut, by causing two ultrasonic beams to traverse the conduit at locations which are spaced apart along the direction of fluid flow. The two ultrasonic signals produced with this arrangement are appropriately conditioned and supplied to a cross-correlator which processes the signals in a manner to produce the desired fluid velocity indication. While such a device produces accurate results, the cross-correlation procedure requires a substantial period of time, so that significant delays exist between a change in flow rate and the production of an indication of such change.